FIG. 1 illustrates a general block diagram showing the relationship of the engine 7, torque converter 10, transmission 8, and differential/axle assembly 9 in a typical vehicle. It is well known that a torque converter is used to transmit torque from an engine to a transmission of a motor vehicle.
The three main components of the torque converter are the pump 37, turbine 38, and stator 39. The torque converter becomes a sealed chamber when the pump is welded to cover 11. The cover is connected to flexplate 41 which is, in turn, bolted to crankshaft 42 of engine 7. The cover can be connected to the flexplate using lugs or studs welded to the cover. The welded connection between the pump and cover transmits engine torque to the pump. Therefore, the pump always rotates at engine speed. The function of the pump is to use this rotational motion to propel the fluid radially outward and axially towards the turbine. Therefore, the pump is a centrifugal pump propelling fluid from a small radial inlet to a large radial outlet, increasing the energy in the fluid. Pressure to engage transmission clutches and the torque converter clutch is supplied by an additional pump in the transmission that is driven by the pump hub.
In torque converter 10 a fluid circuit is created by the pump (sometimes called an impeller), the turbine, and the stator (sometimes called a reactor). The fluid circuit allows the engine to continue rotating when the vehicle is stopped, and accelerate the vehicle when desired by a driver. The torque converter supplements engine torque through torque ratio, similar to a gear reduction. Torque ratio is the ratio of output torque to input torque. Torque ratio is highest at low or no turbine rotational speed (also called stall). Stall torque ratios are typically within a range of 1.8-2.2. This means that the output torque of the torque converter is 1.8-2.2 times greater than the input torque. Output speed, however, is much lower than input speed, because the turbine is connected to the output and it is not rotating, but the input is rotating at engine speed.
Turbine 38 uses the fluid energy it receives from pump 37 to propel the vehicle. Turbine shell 22 is connected to turbine hub 19. Turbine hub 19 uses a spline connection to transmit turbine torque to transmission input shaft 43. The input shaft is connected to the wheels of the vehicle through gears and shafts in transmission 8 and axle differential 9. The force of the fluid impacting the turbine blades is output from the turbine as torque. Axial thrust bearings 31 support the components from axial forces imparted by the fluid. When output torque is sufficient to overcome the inertia of the vehicle at rest, the vehicle begins to move.
After the fluid energy is converted to torque by the turbine, there is still some energy left in the fluid. The fluid exiting from small radial outlet 44 would ordinarily enter the pump in such a manner as to oppose the rotation of the pump. Stator 39 is used to redirect the fluid to help accelerate the pump, thereby increasing torque ratio. Stator 39 is connected to stator shaft 45 through one-way clutch 46. The stator shaft is connected to transmission housing 47 and does not rotate. One-way clutch 46 prevents stator 39 from rotating at low speed ratios (where the pump is spinning faster than the turbine). Fluid entering stator 39 from turbine outlet 44 is turned by stator blades 48 to enter pump 37 in the direction of rotation.
The blade inlet and exit angles, the pump and turbine shell shapes, and the overall diameter of the torque converter influence its performance. Design parameters include the torque ratio, efficiency, and ability of the torque converter to absorb engine torque without allowing the engine to “run away.” This occurs if the torque converter is too small and the pump can't slow the engine.
At low speed ratios, the torque converter works well to allow the engine to rotate while the vehicle is stationary, and to supplement engine torque for increased performance. At speed ratios less than 1, the torque converter is less than 100% efficient. The torque ratio of the torque converter gradually reduces from a high of about 1.8 to 2.2, to a torque ratio of about 1 as the turbine rotational speed approaches the pump rotational speed. The speed ratio when the torque ratio reaches 1 is called the coupling point. At this point, the fluid entering the stator no longer needs redirected, and the one way clutch in the stator allows it to rotate in the same direction as the pump and turbine. Because the stator is not redirecting the fluid, torque output from the torque converter is the same as torque input. The entire fluid circuit will rotate as a unit.
Peak torque converter efficiency is limited to 92-93% based on losses in the fluid. Therefore torque converter clutch 49 is employed to mechanically connect the torque converter input to the output, improving efficiency to 100%. Clutch piston plate 17 is hydraulically applied when commanded by the transmission controller. Piston plate 17 is sealed to turbine hub 19 at its inner diameter by o-ring 18 and to cover 11 at its outer diameter by friction material ring 51. These seals create a pressure chamber and force piston plate 17 into engagement with cover 11. This mechanical connection bypasses the torque converter fluid circuit.
The mechanical connection of torque converter clutch 49 transmits many more engine torsional fluctuations to the drivetrain. As the drivetrain is basically a spring-mass system, torsional fluctuations from the engine can excite natural frequencies of the system. A damper is employed to shift the drivetrain natural frequencies out of the driving range. The damper includes springs 15 in series with engine 7 and transmission 8 to lower the effective spring rate of the system, thereby lowering the natural frequency.
Torque converter clutch 49 generally comprises four components: piston plate 17, cover plates 12 and 16, springs 15, and flange 13. Cover plates 12 and 16 transmit torque from piston plate 17 to compression springs 15. Cover plate wings 52 are formed around springs 15 for axial retention. Torque from piston plate 17 is transmitted to cover plates 12 and 16 through a riveted connection. Cover plates 12 and 16 impart torque to compression springs 15 by contact with an edge of a spring window. Both cover plates work in combination to support the spring on both sides of the spring center axis. Spring force is transmitted to flange 13 by contact with a flange spring window edge. Sometimes the flange also has a rotational tab or slot which engages a portion of the cover plate to prevent over-compression of the springs during high torque events. Torque from flange 13 is transmitted to turbine hub 19 and into transmission input shaft 43.
Energy absorption can be accomplished through friction, sometimes called hysteresis, if desired. Hysteresis includes friction from windup and unwinding of the damper plates, so it is twice the actual friction torque. The hysteresis package generally consists of diaphragm (or Belleville) spring 14 which is placed between flange 13 and one of cover plates 16 to urge flange 13 into contact with the other cover plate 12. By controlling the amount of force exerted by diaphragm spring 14, the amount of friction torque can also be controlled. Typical hysteresis values are in the range of 10-30 Nm.
Turbine shell 22 and pump shell 34 comprise a plurality of slots arranged to engage with turbine blades 23 and pump blades 33, respectively. Each turbine blade and pump blade comprises a blade tab arranged to engage each slot in the turbine or pump shell. The blades are then secured to the shells by an attachment means. Conventionally, the blade tabs are bent once they protrude through the shell. The blades are then usually brazed to strengthen the connection.
In manufacturing the turbine shell and pump shell, manufacturers commonly start with a flat piece of material that is cut in a circular shape. The slots are then punched or cut into the shells in any arrangement suited to engage the blade tabs. The shells are then stamped (or similarly formed) into the semi-toroidal shapes seen most clearly in FIGS. 5 and 6. Such a forming process is disclosed in U.S. Pat. No. 5,868,025 (Fukuda et al.). This forming process deforms the slots and can result in misaligned blades and blade tabs. Thus, the prior art is not able to form a slot shape and width such that their dimensions after the final stamping/forming process are within acceptable tolerance limits to engage with the blades and blade tabs. The largest amount of deformation of the slots occurs in the slots most radially centered. That is, the slots closest to the axis of rotation are most affected by slot deformation during the final stamping process.
Misaligned blade tabs result in poor attachment of a blade to a shell. Poorly attached blades can easily break away from the shell when the torque converter is in use. Thus, misaligned structures are usually scrapped.
To overcome the extent of deformation and scrapped structures, some manufacturers have simultaneously cut slits into the shell and punched the shell into the semi-toroidal shape such as described in U.S. Pat. No. 5,946,962 (Fokuda et al.). However, this process requires a very precise level of control in order to assure slot deformation is within acceptable limits to produce the desired slot widths and shapes.
The brazing process that conventionally follows the above processes includes adding a brazing paste to the blade tabs prior to inserting the blade tabs into the shell slots, and then passing the assembly of shell and blades through a furnace. This is most commonly done using a furnace conveyor belt. The position and level of deformation of the slots can lead to brazing paste leaking through the slots and depositing atop the furnace belt. The deposition of brazing paste leads to delays in factory processes and can result in furnace malfunction.
A method of drastically reducing blade tab attachment deformation is to form indentations arranged to engage blade tabs in lieu of slots. Indents deform much less than slots, especially in the inner radial sections of the shells. A method of forming these indentations by means of stamping or pressing is disclosed in commonly owned U.S. Patent Application No. 2004/0250594 (Schwenk), which is incorporated by reference herein. However, blade tabs for indents are usually smaller in overall dimensions than blade tabs for slots to accommodate the smaller size of the indents. Because the blade tabs for indents do not structurally hold the blades in place against the shell, it is often difficult and not cost effective to only use indents to arrange a plurality of blades against a shell and braze or weld the blades into place. Conventionally, a separate structure is introduced to the blade and shell assembly that is opposite the shell and holds the blade tabs in their respective indents in the shell, so that the blade tabs can be brazed to their respective indentations. However, this process is prone to failure inadequate alignment between blade tabs and indentations.
Accordingly, there is a need for an improved blade attachment means that greatly reduces the blade tab misalignment and increases manufacturability.